Disclosed is an imaging member, and processes for making imaging members. More specifically, illustrated herein is a photoreceptor and a process for preventing or minimizing degradation or loss of integrity of the photoreceptor-substrate interface by incorporating in the photoreceptor an undercoat layer.
An electrophotographic photoreceptor is a device used inside of a xerographic marking system on which a latent image is written by a laser or light emitting diode (LED) bar and then developed with a toner. A photoreceptor comprises for example, a photosensitive layer which may consist of multiple layers including, a charge transporting layer (CTL), a charge generating layer (CGL), an undercoat (UCL) or “blocking” layer, and a supporting substrate layer or base. An overcoat layer (OCL) may also be employed to coat the charge transport layer and protect the charge transport layer and extend the mechanical life of the photoreceptor, in some instances, as much as 10-fold over uncoated photoreceptors of the same make.
Photoreceptor devices under long, repeated use and high stress conditions, such as, high temperature, high relative humidity, and rapid cycling, degrade or lose integrity of the photoreceptor layers. The degradation of the layers of the photoreceptor is observed, for example, as black spots in prints which develop as a result of charge deficient spots and cyclic instability of the photoreceptor. Print defects associated with charge deficient spots, or black spots, are therefore, a major shortcoming in xerographic systems and usually attributed to electrical leakage across the photoreceptor layers at those spots. Although sources of such electrical leakage are multifold, electrical leakage frequently involves degradation of interfaces among the three active layers of the photoreceptor, i.e., undercoat layer, charge generating layer, and charge transporting layer, and in particular, between the undercoat layer and substrate. The degradation induces a conductive path transversal of the photoreceptor and causes the electrical leakage. To minimize degradation, most available methods are directed at improving the composition of the three active layers, individually. The interfaces between the component layers of the photoreceptors often have been ignored because they are inherently difficult to investigate.
Failure can be observed as black spots in prints due to charge deficient spots on photoreceptors was identified using transmission electron microscope analysis of a substrate.
Undercoat layers are used to provide an effective barrier against hole injection from the substrate. Undercoat layers need to permit efficient electron transport at interfaces, and in the bulk of the layer, provide plywood suppression, and provide a barrier against foreign material impaction, as well as have good adhesion properties.
Therefore, charge deficient spots and cyclic stability problems result primarily from degradation of the interface between substrate and undercoat layer. Thus, there is a need to produce photoreceptors which resist degradation of the photoreceptor layers in particular photoreceptors which maintain the integrity of the interface between the substrate and undercoat layer for a prolonged period of time so that the life of photoreceptor can be extended.